1. Field of the Invention
The present invention relates to a finder apparatus for a camera. In particular, the present invention relates to a finder apparatus for a single-lens reflex camera with which an image in an electronic view finder is superimposed on an optical finder image, to thereby enable both the images to be simultaneously visually recognized.
2. Description of the Related Art
In recent years, even a single-lens reflex camera can carry out still image photographing and moving image photographing by using so-called live view display for displaying continuous photographing images by an imaging element on a display unit (display). In this case, a main mirror for guiding light from an object to an optical finder of the single-lens reflex camera is withdrawn from an optical path for the photographing. As a result, a photographer cannot visually recognize an optical finder image, and instead, the photographer views an object image by using the display unit disposed on a camera back surface. However, it is troublesome for the photographer to change a photographer's balance looking into the camera between the optical finder and the display unit. In addition thereto, carrying out the photographing while viewing the display unit with the single-lens reflex camera makes it difficult for the photographer to keep the upper arms holding the camera to the body, which is a drawback leading to the photographing in the photographer's balance easy to vibrate an imaging apparatus. In particular, the hand-held photographing using a telephoto lens without any tripod has been impractical.
In order to cope with this problem, a camera in which the optical finder and the electronic view finder can be switched over has heretofore been proposed. When the optical finder and the electronic view finder can be switched over in the same optical path, the live view display photographing and the moving image photographing using the electronic view finder can be carried out. Moreover, because the photographer's balance looking into the finder of the camera is not different from that in a normal state of using the optical finder, the camera can be held in the ideal posture, to thereby carry out the photographing.
The most realistic unit as a structure which enables the photographer of the camera to observe both the optical finder and the electronic view finder is a structure in which a semi-transmissive mirror (semi-transmissive prism) is disposed between an exit surface of a penta-prism serving as one member of the optical finder, and an eyepiece. With this, a display optical path of the electronic view finder can be introduced from the middle of the optical path of the optical finder.
In addition, in Japanese Patent Application Laid-Open No. 2003-78785, there is proposed a finder apparatus with which an electronic view finder image is displayed so that it is superimposed on the optical finder image. Specifically, a liquid-crystal filter is disposed in the finder optical path so that an amount of light of an optical object image is variable, and brightness of a display panel of the electronic view finder is changed, to thereby enable an amount of light of an electronic image to be superimposed to be changed. In addition, in Japanese Patent Application Laid-Open No. 2003-78785, there are described various display state modes such as an optical finder mode in which no electronic image is displayed, a superimpose display mode in which an electronic image is displayed so that it is superimposed on an optical image, and an image confirming mode in which data on only an electronic image obtained through the past photographing is read out to display only the electronic image. In Japanese Patent Application Laid-Open No. 2003-78785, it is also disclosed that the optimum finder display is realized depending on those modes, and a structural example in which this structure is applied to the single-lens reflex camera.
In Japanese Patent Application Laid-Open No. 2003-78785, a structural example of a finder of the single-lens reflex camera is described as follows with which the image in the electronic view finder is displayed so that it is superimposed on the optical finder image, and hence both the images can be simultaneously visually recognized.
(1) In Optical Finder Mode
In an optical finder mode in which no electronic image is displayed, a control circuit stops an imaging element and a signal processing circuit. As a result, an electronic image display function thoroughly becomes a non-operation state. At this time, a liquid-crystal filter is set to a transparent state (having transmissivity of 100%).
(2) In Superimpose Display Mode
In a superimpose display mode in which the electronic image is displayed so that it is superimposed on the optical image, the imaging element, the signal processing circuit, and the like are continuously operated to display a moving image on a liquid crystal monitor. At this time, the liquid-crystal filter is set to a semi-transmissive state (having transmissivity of 50%). In this case, when the brightness of the object is low, it is expected that the optical image cannot be visually recognized in some cases. On the other hand, it is also expected that the reduction of 50% is insufficient. Then, the brightness of the object is measured and the transmissivity is changed in accordance with the value of the brightness, and hence a stable finder image is always obtained. In addition, the balance may be relatively kept by adjusting a light amount of a backlight unit.
(3) In Reproduction Mode
In the image confirming mode in which the data on the electronic image obtained through the past photographing is read out to display only the electronic image, the imaging element is stopped, and the data on the last photographing image is read from an image memory into the signal processing circuit to display the still image on the liquid crystal monitor. At this time, the liquid crystal finder is set to a non-transparent state (having the transmissivity of 0%).
As described above, in Japanese Patent Application Laid-Open No. 2003-78785, there is proposed the control under which the transmissivity of an object light dimming unit including a liquid-crystal filter is changed in accordance with the various finder display modes of the camera, and at the same time, the light amount of a backlight unit of the liquid crystal monitor is also changed, to thereby provide the optimum finder display. However, the light dimming control by the liquid-crystal filter is insufficient for obtaining an optical finder image having an excellent appearance quality from a viewpoint of the characteristics of the liquid crystal device itself. In a general TN liquid crystal panel, in principle, the transmissivity of 50% or more cannot be obtained because a polarization plate is used. The sight of the optical object image becomes dark in any of the photographing environments other than the outside, namely, a high-brightness photographing environment, and hence the visibility of the photographing object is reduced.
In addition, when a PN liquid crystal (polymer-dispersed liquid crystal) panel is used in the light dimming unit, the transmissivity at drive of the liquid crystal is as high as approximately 90%. However, there is caused a problem in that when the light is diffused and dimmed at non-drive of the liquid crystal, the optical image itself is diffused, and hence the object image is not sharply viewed. In addition, using the liquid crystal device leads to a problem of the increase in size and cost of the camera on which the liquid crystal device is to be mounted.